Castle Point ASSI

The limestone rocks exposed in the cliffs and rock platforms between Ballycastle Harbour and Port Calliagh belong to the Ulster White Limestone Formation and are overlain by basalt of the Antrim Lava Group. The Ballycastle and Port Calliagh Chalk Members have their type localities within the site. The available evidence indicates the Chalk Members were deposited in a warm, shallow sea during the Cretaceous, some 80 million years ago. They represent the youngest Cretaceous (Campanian to Maastrichtian) strata preserved in Northern Ireland (and indeed in Ireland) with the Ballycastle Chalk Member being the younger of the two.

At the eastern end of the site there is an exposure of the Ballycastle Pellet Chalk. The available evidence indicates that the Pellet Chalk was derived from the Ulster White Limestone Formation as a colluvial, or gravity induced, deposit that accumulated at the foot of a basalt-capped chalk slope. This is much softer than the ‘normal’ well cemented Ulster White Limestone Formation members.
Consequently it is one of the only localities that readily yield microscopic marine fossils, or foraminiferans, of this age. The taxa Globorotalites conicus and Neoflabellina rugosa, which are unrecorded post Campanian, and Osangularia lens which is exclusively Maastrichtian, indicate the rocks span the Campanian – Maastrichtian boundary.

There is another exposure of the Pellet Chalk further north west along the coast. This is pinkish and is found in association with an area of brecciated limestone with large, round boulders of basalt and broken flints embedded in it. There is a circular depression at the southern end of the exposure and this has been interpreted as an erosional feature that subsequently became filled with the debris forming the breccia and Pellet Chalk. Furthermore, a volcanic vent breccia can be seen in the cliff section adjacent to it, cutting through the basalt above the limestone.
The area is also notable for its inter-tidal communities. An extensive limestone, wave cut platform on a moderately exposed shore supports many wide shallow rock pools. The intertidal area is characterised by red algae and patellobarnacle biotopes although barnacles themselves are scarce due to the soft nature of the substrate. Pockets of localised shelter allow the growth of spiral wrack seaweed.

Site Related Documents

Site map (.PDF 625Kb), Citation document (.PDF 80Kb) and Views about Management document (.PDF 90Kb).